Hermetic sealing device

ABSTRACT

[Configuration] In a hermetic sealing device provided with a thread on an atmosphere side sliding surface of a sealing lip that is in sliding contact with a rotating shaft, the atmosphere side sliding surface of the sealing lip is formed into a large curve that passes a sealing lip tip and recedes from a surface of a component with which the lip is in sliding contact towards the atmosphere side. A thread with a triangular cross-section is formed connecting the lip tip to a projecting section of a predetermined height formed at a required position distant from the lip tip. A ridge line of a thread peak of the thread is formed linearly. A thread is formed on the atmosphere side sliding surface, configured such that the height of the thread peak gradually increases away from the lip tip. 
     [Effect] Because the ridge line of the thread peak is linear, a space between the shaft and the sealing lip can be maintained. As a result, risk of infiltrating dust being guided to a contacting section of the sealing lip tip can be suppressed, and leakage caused by dust becoming caught in the sealing lip can be prevented.

TECHNICAL FIELD

The present invention relates to a hermetic sealing device, such as anoil seal with a screw, that seals a ring-shaped space between twocomponents assembled such as to rotate freely in relation to each other.

BACKGROUND ART

As a type of hermetic sealing device such as this, a hermetic sealingdevice is conventionally known in which a thread projection is formed onan atmosphere side sliding surface of a sealing lip, the sealing lipbeing in sealing contact with an outer circumferential surface of arotating shaft of a ring-shaped seal main body such as to rotate freely.Sealing performance is enhanced by a pumping effect achieved by thethread projection. However, although parallel thread projections havingconstant height and width can ensure initial sealability, a problemoccurs in that the effect of the thread deteriorates when the sealinglip becomes worn over time.

A hermetic sealing device is proposed in which a thread provided on anatmosphere side sliding surface of a sealing lip is shaped such that auniformly shaped sub thread having an almost constant height iscontinuously formed on the lip tip side of a main thread. A main threadbecomes larger from the sub thread towards the atmosphere side, andcontact width increases over time in use. In the above-describedhermetic sealing device, the uniformly shaped sub thread having analmost constant height is continuously formed on the lip tip side of themain thread provided on the atmosphere side sliding surface of the lip.The height of the thread peak of the main thread gradually increasesfrom the sub thread towards the atmosphere side, ensuring contact lengthof the thread when wear occurs over time in use. The hermetic sealingdevice is effective in terms of preventing deterioration of sealabilitycaused by wear of the sealing lip, and maintaining the effect of thethread at an initial stage and over a long period (refer to PatentLiterature 1).

As a hermetic sealing device similar to that described in PatentLiterature 1, an oil seal with a screw shown in FIG. 6 and FIG. 7 isproposed. In the oil seal with a screw, two types of threads 102 and 103are alternately provided on a sealing surface 101 at a predeterminedangle of tilt K. The threads 102 and 103 achieve a pumping effect inwhich lubricating oil or the like that attempts to leak from the sealedside OS to the atmosphere side is constantly retained on the sealedside. The height of one thread 102 is constant. The other thread 103 isa stepped thread, in which a height h1 in an area near a lip tip 104 isa low height equivalent to that of the thread 102, forming a lowprojecting section 103 a. A height h2 in an area distant from the liptip 104 is higher than the low projecting section 103 a, forming a highprojecting section 103 c. The low projecting section 103 a and the highprojecting section 103 c are connected by an angled section 103 b (referto Patent Literature 2).

-   Patent Literature 1: Japanese Patent No. 3278349-   Patent Literature 2: Japanese Patent Laid-open Publication No.    2001-173798

When the stepped thread provided with a main thread and a sub thread,described in Patent Literature 1 and Patent Literature 2, is used, in aninitial stage of use when the lip tip 104 that is in an unworn state ora slightly worn state comes into contact with a rotating shaft 106, astrong pumping effect can be achieved by the thread 102 having aconstant height and the low projecting section 103 a of the steppedthread 103. When wear of the lip tip progresses, the angled section 103b and the high projecting section 103 c that are higher than the lowprojecting section 103 a of the stepped thread 103 gradually come intocontact with the rotating shaft 106. Therefore, the height from thesealing surface 101 of the screw 103 contacting the rotating shaft 106gradually increases, strengthening the pumping effect by which thesealed fluid that attempts to leak is constantly positioned on thesealed side OS. Stable sealability can be maintained.

However, in the thread projections described in Patent Literature 1 andPatent Literature 2, with the atmosphere side sliding surface 101serving as a base surface, the height of the thread peak in relation tothe base surface 101 (atmosphere side sliding surface) is stepped,forming the low projecting section 103 a, the angled section 103 b, andthe high projecting section 103 c. Therefore, when the seal main body ismounted on the shaft 106, as shown in FIG. 8, a space between the shaft106 and the angled section 103 b of the stepped thread becomes narrow inthe mounted state. The space becomes even narrower at the low projectingsection 103 a.

As a result, when dust infiltrates the atmosphere side sliding surface101 from outside, high-speed rotation of the rotating shaft 106 causesthe dust to scatter while being rotated around the rotating shaft 106.The dust is guided between the angled section 103 b and the rotatingshaft 106 while colliding with the surface of the high projectingsection 103 c of the stepped thread. Furthermore, the dust collides withthe angled section 103 b and is guided along the angled section,entering the narrow space between the low projecting section 103 a andthe rotating shaft 106. The dust becomes caught in the lip tip section,and a problem occurs in that there is risk of oil leakage.

A solution to the above-described problem is to increase the sealingangle midway, rather than increasing the height of the thread peak. Whenthis solution is used, the thread peak becomes gradually higher as aresult, and an effect similar to that of the above-describedconventional Patent Literature 2 can be expected. However, in thisinstance, a bending point is formed at a point of change at which thesealing angle is increased midway. When wear progresses to the bendingpoint, a problem occurs in that sealability becomes unstable.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

The present invention has been achieved in light of the above-describedproblems. An object of the present invention is to form a change in asealing angle of a lip tip section by use of a large curve, rather thanconfiguring the sealing angle by two surfaces, and to use a straightline to form a ridge line of a thread peak, thereby eliminatinginstability caused by angle change.

Means for Solving Problem

To achieve the above-described object, a hermetic sealing device of thepresent invention is a hermetic sealing device that seals a ring-shapedspace between two components assembled such as to rotate freely inrelation to each other. The sealing device includes a ring-shaped sealmain body assembled to one component of the two components and a threadon an atmosphere side sliding surface of a sealing lip included in theseal main body that is in sliding contact with the other component ofthe two components. The atmosphere side sliding surface of the sealinglip is formed into a large curve passing a sealing lip tip and recedingfrom a surface of the component with which the lip is in sliding contacttowards the atmosphere side. A thread is formed on the atmosphere sidesliding surface, connecting a low projecting section at the lip tip to ahigh projecting section having a required height provided at apredetermined position distant from the lip tip. A ridge line of athread peak of the formed thread is linear.

Effect of the Invention

In the hermetic sealing device of the present invention, an atmosphereside sliding surface of a sealing lip is formed by a large curve thatpasses a tip of the sealing lip and recedes from a surface of acomponent with which the lip is in sliding contact towards theatmosphere side. With a height of a projecting section of a thread at apredetermined position distant from the lip tip being a desired height,the thread formed on the atmosphere side sliding surface is formedconnecting the lip tip to the high projecting section having desiredheight. A ridge line of a thread peak of the thread is linear. A threadis formed such that the height of the thread peak gradually increasesaway from the lip tip. Because the atmosphere side sliding surface isformed by a large curve passing the tip of the sealing lip as describedabove, instability caused by an angle change in the sealing angle can beeliminated.

In addition, when an oil seal main body is assembled to a shaft, becausethe ridge line of the thread peak is linear as described above, aportion at which the thread approaches the shaft is not formed on theshaft as well. Therefore, a space between the shaft and the sealing lipcan be maintained. As a result, risk of infiltrating dust being guidedto a contacting section of the sealing lip tip can be suppressed. Aneffect can be achieved in that leakage of a sealed fluid accompanyingdamage to the lip caused by dust being caught in the sealing lip can beprevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a half cross-sectional view of a hermetic sealing deviceaccording to an embodiment of the present invention.

FIG. 2 is an enlarged explanatory diagram of an atmosphere side slidingsurface and a thread.

FIG. 3 is an enlarged cross-sectional view taken along line A-A in FIG.2.

FIG. 4 is an explanatory diagram of a state of the thread duringmounting to a shaft.

FIG. 5 is an explanatory diagram of a relationship between lip wearwidth, back leakage wear width, and back leakage amount of a productaccording to the embodiment of the present invention and a conventionalproduct.

FIG. 6 is an enlarged explanatory diagram of a thread of a conventionalexample.

FIG. 7 is an enlarged cross-sectional view taken along line B-B in FIG.6.

FIG. 8 is an explanatory diagram of the conventional example duringmounting on a shaft.

EXPLANATIONS OF LETTERS OR NUMERALS BEST MODE(S) FOR CARRYING OUT THEINVENTION

An embodiment of the present invention will be described. In FIG. 1, anoil seal 1 has a seal main body 2 that is mounted on one component, suchas a housing, of two components that rotate in relation to each other,and a sealing lip 4 that slides over and is in sealing contact with ashaft 3 that is the other component. A thread 6 is formed on anatmosphere side sliding surface 5 of the sealing lip 4 at apredetermined angle O.

The seal main body 2 is made of a metal reinforcing ring 7 having anL-shaped cross-section and a rubber elastic body 8. The rubber elasticbody 8 is burned onto the outer peripheral portion of a cylindricalsection 9 of the metal reinforcing ring 7 and the outer periphery of aflange section 10 of the metal reinforcing ring 7. The sealing lip 4 isprovided on the sealed fluid side of an inner end of the flange section10 of the metal reinforcing ring 7, and a dust lip 11 is provided on theatmosphere side. The sealing lip 4 is in sliding contact with the shaft3 and achieves a sealing effect. The dust lip 11 is in contact with theshaft 3 and prevents infiltration of dust on the atmosphere side. Aspring 12 is mounted on the outer periphery of the sealing lip 4 to addstraining force onto the shaft 3.

The atmosphere side sliding surface 5 of the sealing lip 4 according tothe embodiment is formed by a curve 15 having a large diameter R. Thecurve 15 passes the tip of the sealing lip 4 and recedes from thesurface of the component with which the lip 4 is in sliding contacttowards the atmosphere side. The atmosphere side sliding surface 5 isconfigured by a sloped surface that is sloped by the large curve 15protruding in an R-shape from the tip of the sealing lip 4 towards thebase portion of the sealing lip 4. A portion of the sealing lip 4 on thetip section side slides over the shaft 3. The thread 6 is provided onthe atmosphere side sliding surface 5 that is formed by the large curve15, described above. Sealing performance is enhanced by a pumping effectof the thread 6. The thread 6 is formed at a predetermined angle θ onthe atmosphere side sliding surface 5 formed by the curve 15 having alarge diameter R, described above. The cross-section of the thread 6 isan almost triangular peaked shape with an angle of about 90 degrees. Thethread 6 is formed including a low projecting section 16 where thethread height at the tip of the sealing lip 4 is H1 and a highprojecting section 17 of which the height of a projecting section of thethread at a required position distant from the tip of the lip 4 is adesired height H2 higher than the height H1 at the tip section. Thethread 6 is formed connecting the lip tip of the low projecting section16 having the thread height of H1 to the high projecting section 17having the height H2. A ridge line 18 of the thread peak of the formedthread is formed linearly. As a result of the ridge line 18 of thethread peak being linear, in conjunction with the atmosphere sidesliding surface 5 being the large curve 15, the thread is configuredsuch that the height of the thread 6 gradually increases away from thelip tip. In addition, the thread width gradually widens from the tip.

The above-described thread according to the embodiment will be furtherdescribed in detail. As shown in FIG. 3, at the tip of the sealing lip4, the large-diameter curve 15 passes the tip. Therefore, although thethread height at the tip of the sealing lip 4 is H1, because theatmosphere side sliding surface 5 at the tip section of the sealing lip4 is the curve 15 having a large diameter R, the height of the threadpeak is not constant on the atmosphere side of the tip of the sealinglip 4. The thread height begins to gradually increase immediately fromthe tip section. As described above, as a result of the curvedatmosphere sliding surface 5 having a large diameter R and the linearridge line 18, the height of the thread peak at the tip section of thesealing lip 4 gradually increases away from the tip.

In this way, according to the embodiment, the atmosphere side slidingsurface 5 serving as a base surface of the thread 6 has a curved shapewith a large diameter R, and a sealing angle change is formed at the tipsection of the sealing lip 4 by a large curve. As a result, instabilitycaused by angle change can be eliminated. In addition, the ridge line 18of the thread peak is formed linearly, and the atmosphere side slidingsurface 5 is formed into a large-diameter curve passing through the tipof the sealing lip 4, as described above. Therefore, the thread heightis configured to gradually increase immediately from the atmosphere sidesliding surface 5 serving as the base.

In the hermetic sealing device according to the embodiment, thespiral-shaped thread 6 is provided connected to the tip of the sealinglip 4 on the atmosphere side sliding surface 5 on the inner side of thesealing lip 4 in the radial direction, the sealing lip 4 havingelasticity. Therefore, the tip of the thread 6 comes into contact withthe shaft 3 in a mounted state. In an initial stage of use when thesealing lip 4 is not worn, the lip tip comes into contact with the shaft3, exerting a pumping effect in which sealed fluid that attempts to leakfrom the sealed side towards the atmosphere side is constantlypositioned on the sealed side.

When the wear of the tip of the sealing lip 4 progresses with use, thethread 6 of which the height gradually increases from the height H1 ofthe thread 6 comes into contact with the shaft 3. Therefore, the heightfrom the atmosphere side sliding surface (sealing surface) 5 of thethread 6 in contact with the shaft 3 gradually increases, graduallystrengthening the pumping effect in which the sealed fluid that attemptsto leak is constantly positioned on the sealed fluid side. A stablesealing effect can be achieved.

In the above-described usage state, when the oil seal 1 is mounted on ahousing (not shown), and the sealing lip 4 of the oil seal 1 is insealing contact with the shaft 3, as shown in FIG. 4, because the ridgeline 18 of the thread peak is linear, a constant space can be maintainedin relation to the shaft 3, without the thread peak approaching theshaft 3. Because a stepped guiding section such as that which guidesdust entering between the lip and rotating and scattering around theperiphery of the shaft rotating at high speed to a contacting section ofthe lip tip is not included according to the embodiment, the risk ofdust being guided to the lip tip section can be suppressed.

TABLE 1 Seal durability against foreign matter within oil Test NameConfirmation of durability against foreign matter within oil Shaftmisalignment 0.2 mm (run-out width) Mounting misalignment ↑ Revolution6000 rpm Testing temperature 130° C. Oil used Oil side: degraded oilTest duration Until leakage Conventional product Present inventionSample Material 1 Material 2 Material 1 Material 2 Main lip Before testØ78.48 Ø78.42 Ø78.30 Ø78.25 inner After test Ø78.91 Ø78.94 Ø78.99 Ø79.04diameter Retained 1.09 1.06 1.01 0.96 (mm) interference Main lip Beforetest 20.9 21.2 20.6 20.9 straining After test 17.5 17.5 17.2 16.9 force(N) Amount of −3.4 −3.7 −3.4 −4 change Main lip Max. 0.78 0.75 0.71 0.82wear Min. 0.63 0.57 0.62 0.65 width Ave. 0.71 0.68 0.67 0.74 (mm) ShaftMax. 170 163 175 182 wear (μm) Min. 153 145 159 161 Ave. 161 157 167 172Test result Leakage Leakage Leakage Leakage at 501 h at 495 h at 512 hat 585 h

In Table 1, two samples each of a seal described according to theembodiment of the present invention and a conventional product describedin Patent Literature 2 were respectively evaluated as Material 1 andMaterial 2 for seal durability against foreign matter within oil.

In Table 1, the time elapsed until oil leakage occurs is examined usingdegraded oil, with a shaft misalignment of 0.2 mm in run-out width, arotation frequency of 6000 rpm, and a testing temperature of 130° C. Asshown in Table 1, there is little difference in the wear width and thewear depth of the lip between the seal described according to theembodiment of the present invention and the conventional product.Rather, compared to the conventional product, the time elapsed untilleakage is slightly longer. The product according to the embodiment ofthe invention compares favorably with the conventional product.

TABLE 2 Seal durability against foreign matter on atmosphere side TestName Confirmation of durability against foreign matter on atmosphereside Shaft misalignment 0.2 mm (run-out width) Mounting misalignment ↑Revolution 4000 rpm Testing temperature 130° C. Oil used Oil side:engine oil; Atmosphere side: dried dust (Dust: 80% of JIS type 8 and 20%of JIS type 1) 5 vol % Test duration 100 h/200 h or until leakageConventional product Present invention Sample 100 h 200 h 100 h 200 hMain lip Before test Ø78.28 Ø78.25 Ø78.31 Ø78.33 inner After test Ø78.58Ø78.61 Ø78.38 Ø78.44 diameter Retained 1.42 1.39 1.62 1.56 (mm)interference Dust lip Before test Ø80.52 Ø80.51 Ø80.41 Ø80.41 innerAfter test Ø80.52 Ø80.52 Ø80.45 Ø80.45 diameter Amount of 0 0.01 0.040.04 (mm) change Main lip Before test 21.4 21.9 20.9 21.2 strainingAfter test 18.8 18.2 18.8 17.9 force (N) Amount of −2.6 −3.7 −1.2 −2.7change Main lip Max. 0.42 0.41 0.13 0.26 wear Min. 0.31 0.32 0.07 0.13width Ave. 0.35 0.36 0.10 0.18 (mm) Test result Leakage Leakage No No at23 h at 23 h leakage leakage at 100 h at 200 h

In Table 2, two samples each of the conventional product and the sealdescribed according to the embodiment of the present invention wererespectively evaluated as Material 1 and Material 2 for seal durabilityagainst foreign matter on the atmosphere side.

In Table 2, the test was conducted for 100 hours or until leakageoccurred, with a shaft misalignment of 0.2 mm in run-out width, arotation frequency of 4000 rpm, a 200-hour testing temperature of 130°C., engine oil placed on the oil side, and dried dust placed on theatmosphere side. The conventional product started to leak at 23 hours.The product according to the embodiment of the present invention did notleak even after the elapse of 100 hours or 200 hours because, asdescribed above, regarding infiltration of dust, the dust is not guidedto the lip side. As a result, it has been proven that the productaccording to the embodiment of the present invention is significantlysuperior regarding durability against dust, compared to the conventionalproduct.

FIG. 5 is a graph indicating the wear width of the lip and a backleakage amount (suction amount). In the conventional product, it can beseen that the amount of suction decreases as the wear width of the lipincreases. This indicates deterioration of sealability. According to theembodiment of the present invention, little change is found in thesuction amount even when the wear width of the lip increases.Sealability does not change, and favorable sealability can bemaintained.

As described above, according to the embodiment of the presentinvention, the atmosphere side sliding surface 5 is formed by thelarge-diameter curve 15 passing the lip tip. The ridge line 18 of thethread peak of the thread 6 provided on the sliding surface 5 is formedlinearly. Therefore, when the seal main body is mounted on the rotatingshaft 3, because the ridge line 18 of the thread peak is formed linearlyas described above, there is nothing present that acts as a factor forguiding dust between the rotating shaft 3 and the thread 6. Dust is notguided to the sealing lip tip, and sealability is not impaired.

1. A hermetic sealing device that seals a ring-shaped space between twocomponents assembled such as to rotate freely in relation to each other,the sealing device comprising: a ring-shaped seal main body assembled toone component of the two components; and a thread on an atmosphere sidesliding surface of a sealing lip included in the seal main body that isin sliding contact with the other component of the two components,wherein the atmosphere side sliding surface of the sealing lip is formedinto a large curve passing a sealing lip tip and receding from a surfaceof the component with which the lip is in sliding contact towards theatmosphere side, a thread is formed on the atmosphere side slidingsurface, connecting a low projecting section at the lip tip to a highprojecting section having a required height provided at a predeterminedposition distant from the lip tip, and a ridge line of a thread peak ofthe formed thread is linear.